Types of Golf Cart Batteries

Golf cart batteries remained roughly the same for many years, but it is all changing now. The traditional batteries used are known as lead-acid batteries. They have lead cells that are flooded with an electrolyte that is comprised of water and sulfuric acid and have a vent in the cap on top of each cell that lets the battery “breath” as the charging is taking place. I’ll refer to this type of battery as being a “standard” battery. They are still being used in many carts (even some new ones) as the transition takes place, but I think their days are numbered. They work quite well, but have some limitations, also.

Weight is probably the biggest issue with the lead-acid golf cart battery. A single lead-acid cell is capable of being charged to about 2.15 volts, so they are commonly packaged in groups of 3 cells in series (for what is called a 6 volt battery). Obviously, when it is fully charged, its voltage would be closer to 6.45 volts (typically more like 6.3, under normal circumstances). Another popular packaging consists of 4 cells to form an 8 volt battery (around 8.4 volts when fully charged). Likewise, some are packaged in groups of 6 cells to form a 12 volt battery (around 12.7 volts when fully charged). A typical 6 volt battery weighs around 62 lbs., a typical 8 volt battery weighs around 72 lbs., and a typical 12 volt battery weighs around 82 lbs.

In order to supply enough voltage to efficiently operate a golf cart’s motor (which requires a higher voltage), the batteries are usually placed in a series combination to achieve either 36 or 48 volts (6-6 volt batteries for 36 volts, 6-8 volt batteries for 48 volts, 4-12 volt batteries for 48 volts, or even 8-6 volts batteries for 48 volts). So, as you can see, to fit that many batteries in the cart adds several hundred lbs. to the total weight of the cart. Not only do they make for a heavy cart, but if you are the guy who has to place the batteries in the cart or replace them as they go bad, you’ve got some hard work to do. I worked on these critters for many years and I am now pretty much disabled with back problems. 

Another issue with lead-acid batteries, is their need to be maintained. There is a liquid inside of the batteries called an electrolyte, that needs to have its level maintained consistently. As the batteries are cycled (charged and discharged time after time), some of the electrolyte disappears. Since the electrolyte needs to cover the plates within the battery at all times, any exposure of the plates to air (because they are not covered by electrolyte) becomes a very detrimental problem for the batteries. A process called “sulfation” that occurs within the batteries as they are cycled is amplified, and will soon damage the batteries to where they cannot receive a proper charge so they don’t work like they were designed to and eventually need to be replaced.

The price to replace a set of standard batteries is not cheap and can approach or even exceed $1000, depending on the cart’s configuration.

Through the years, there have been batteries developed that still use lead-acid technology, but with different types of electrolytes systems:

AGM (absorbed glass mat). This type of battery is usually more expensive than standard batteries. They can typically be used with the battery charger that came with the cart (which we will go into detail about a little later). They are probably the least expensive option to standard lead-acid batteries and offer “maintenance free” operation. They are a sealed, so there is no need to ever add to the electrolyte. They are considered to be a type of VRLA (valve regulated lead-acid battery).   

Gel Filled. These are a another VRLA type of battery and can work well in a golf cart, but they require a special charger. They have slightly different operational characteristics than regular lead-acid or AGM batteries, but can actually be used in a broader range of uses than just for golf carts. They are generally more expensive than either of the above.

A relatively new type of battery to find its way into the golf cart market is the lithium-ion type. It is NOT a lead-acid battery but, operates on a totally different technology. I think the lithium-ion batteries will completely take over the market eventually because of all the advantages they offer. Among these advantages are:

                Much lighter than standard or AGM or Gel Filled

                Can be charged much faster

                Last much longer (generally come with at least a 5 year warranty, maybe even longer)

                Like AGM and Gel Filled, they are maintenance- free

They operate with the same efficiency over the entire discharge cycle (same amount of power right up until they are totally discharged)

Can last up to 5000 cycles (charged and discharged) instead of the 500 cycles that is typical with lead-acid batteries

The main DISADVANTAGE of the lithium-ion batteries is that they cost quite a bit more than lead-acid batteries. They can cost up to 2 or 3 times that of a standard battery.

Unfortunately, lithium-ion batteries have a tendency to catch fire and even blow-up unless certain precautions are observed during the charging process. Because of this, each lithium-ion golf cart battery has its own “Battery Management System” (BMS) or “Battery Protection System” (BPS) built into it.

What I really want to discuss in this article, is how all of these types of batteries affect getting them properly charged.

The original type of charger that came with a golf cart years ago, had NO “intelligence” with which to make decisions about how much voltage or current to make available to the batteries during the charge cycle. They were comprised of a simple “ferro-resonate” transformer, a capacitor that was part of the “ferro-resonate” circuitry, a diode system to rectify alternating current to direct current, a circuit breaker or fuse of some type, a meter to monitor haw much current was being drawn, and a manually operated timer that set how long the charger would remain on.

With this type of charger, the amount of voltage and current that was available to the batteries was only set by the limitations of the charger and by the impedance (resistance to current flow) of the batteries. When you first connected the charger to the battery pack and set the mechanical timer to start the charge cycle, the batteries (in their discharged state) offered very little resistance to current flow, so, you would see the current meter go to the high end of the scale. This all goes back to the science behind Ohm’s Law, which says that the current flow through a circuit is equal to voltage made available divided by the resistance of the circuit.

I = E/R,  where I is the current stated in amperes (amps), E is the voltage which is stated in volts, and R is the resistance (impedance) which is stated in ohms.

So, as the battery pack began to charge, and the batteries became less depleted of energy, the resistance of the battery pack would begin to rise. As R went up, I went down. As the batteries continued to charge, the R continued to go higher and higher until they finally represented a lot of resistance to the circuit and I went way down. The changing resistance of the batteries was the only controlling aspect of the system (other than the built in limitations of the charger). The problem with this system is obvious. Who knows how long to set the timer for? If the charger doesn’t get shut off when the batteries are charged, the charger just keeps trying to add more energy to them even though they don’t want anymore. The result could damage the batteries permanently and even “boil” the electrolyte out, leaving the cells to sulfate at a rapid rate. Now, if you sat and watched the current meter during the whole charge cycle, you could determine when the current flow dropped off to between 5 and 8 amps (indicating that the batteries were getting closer to charged), leave the charger on for another hour or so to ensure what is called equalization (we’ll get to that later), and then shut the timer off. But who the heck is going to do that?

The next step in the evolution of the chargers was to add a circuit board within the charger that would do more or less what I described above (monitoring the current flow) and then automatically shut the charger off, before any damage was done to the batteries. This was a big improvement and became the “state of the art” for chargers for a long time. Even though the circuit board monitored the current, it still didn’t do anything to “regulate” the current flow or the voltage that was made available in the process of charging the batteries. The circuit board did NOT have a microprocessor that could be programmed. The circuitry on the board contained only transistors, logic comparators, diodes, capacitors and resistors, etc.

Then, the whole picture changed when they started building “smart” chargers that could not only monitor the charge operation, but could be programmed to regulate current flow and voltages applied during the cycle. It had been discovered that by controlling different phases of the charge operation, a more efficient charge could take place, thereby providing better operation of the golf cart longer battery life as well.

Most smart chargers divide the charge cycle into at least three stages : Bulk, Absorption, and Float. It’s important to realize that different charger manufacturers handle things a little differently, but the following is a GENERAL description of what takes place in these stages of charging:

Bulk      

The Bulk stage takes place during about the first 80% to 90% of the charge cycle. In this stage, current that is made available to the batteries is generally only limited by what the charger can safely supply. If, for instance, you have a 25 amp charger, you’ll see the meter jump way up to close to 25 amps. If you also had a voltmeter across the battery pack (and you usually don’t) you would see the voltage start out low and build up as the charge continues. The charger tries to maintain as much current flow as is safely possible as the voltage comes up.

Absorption

Once the battery pack reaches a threshold voltage (usually referred to as “the absorb voltage”), the charger holds its voltage output at that level, instead of letting the voltage continue to rise while it lets current continue to flow. The amount of current flow keeps decreasing as the charge nears completion. This threshold voltage is very important, as it must be SAFE for the batteries and varies for different types of batteries. For a standard set of golf cart batteries, it is usually around 43.2 to 44.4 volts. But for a set of sealed batteries, such as AGM, it is much less and usually held to around 43.8 to 44.3 volts. For a set of Gel Filled batteries the voltage must be held even lower to around 42.6 to 42.9. At this point we start to see that the charger needs to be “matched” to the battery type. That’s why so many new batteries are ruined in short order when they are used to replace standard batteries. They do NOT get charged correctly. If this threshold voltage is held too high, the batteries can overheat and even explode.

Float

In this stage, the charger reduces its voltage to a number that pretty much coincides with the peak voltage that the battery pack would measure, fully charged, without a load (just sitting there). This is usually around 39.6 to 40.2 volts. Many of the later model smart chargers (when left connected to the cart) will even tun off and on automatically to maintain this voltage when left unattended. It is sort of like what is called a trickle charge. Since the batteries are already charged, their impedance is quite high, and only a trickle of current will flow.

At this point, I should mention the term “equalization”. Some manufacturers refer to all or part of the float cycle as being an equalization stage, but there are different opinions of that.

Most engineers agree that equalizing lead-acid batteries is a process in which the batteries are intentionally overcharged (slightly and in a controlled fashion) in order to help de-sulfate the plates. Some of the smart chargers include an additional stage to their charge cycle to accommodate this, but many do not.

 Lithium-ion batteries have even different characteristics and need a bit of special consideration. I mentioned earlier that lithium-ion batteries have a tendency to catch fire or even explode unless strict control of current flow is maintained during the charge cycle. To accomplish this control, each battery has its own circuit board built into the package of the battery to protect it. Without going into all of the details of the lithium-ion battery operation, it is generally accepted by lithium-ion golf cart battery manufacturers that a charger built to be used on the SLA batteries (AGM and Gel Filled) can be used without harming the batteries. However, they will not perform the “rapid recharge” that is possible with a charger that is built specifically for lithium-ion batteries. For instance, where a standard battery pack would take around 6 to 8 hours (if 50% discharged), a lithium-ion pack could be charged in perhaps 2 to3 hours with a battery charger designed specifically for lithium-ion batteries.

In Conclusion

When selecting a charger for a specific battery type, it is important to consider what the operation of the charger is going to look like. Some chargers now have ways to put them in different modes of operation to match that required by the type of batteries being used. One size doesn’t fit all, anymore. In order to end up with the correct charger for the batteries that you are working with, the documentation for the charger and the batteries need to be studied and observed. Some chargers have to be ordered specifically for certain types of batteries, but some use small switches (called DIP or dual in-line pin switches) located on either the back of the charger or even inside the charger to “select” the proper function of the charger that matches specific batteries you are going to charge with it. Some are even so sophisticated as to allow the user, through bluetooth technology, set the proper charger “profile” for the batteries with your cell phone.

Indeed, the evolution of batteries and chargers has come a long way. There is bunches of information on the internet regarding them, and I encourage you to learn all you can about the battery type you are going to use, and how to accommodate its charging.

Ron Staley has published the following books, and you can get more information about them by just clicking on each title below:

Electric Golf Cart Repair 101 (and a half)

                Techniques, Tips, Tools and Tales

Gas Golf Cart Repair 101 (and a half)

                Techniques, Tips, Tools and Tales

Suck, Squish, Boom and Blow

                4-Stroke Golf Cart Engines Explored

Those Darned Slot Machines

                What Makes Them Tick

                By an old Slot Machine Mechanic

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